Synoptic Climatology of Pre-Monsoon Severe Lightning Events in Bangladesh

Abstract

In Bangladesh, 1073 lightning deaths are reported only in May from 2010 to 2021 that accounts 34% of the total lightning death. The mean thunderstorm days are the maximum in Sylhet that accounts 9.46, 19.27, and 21.67 from March through May with the mean lightning frequency of 29.11, 70.50, and 82.55. Seasonal average temperature difference between winter and pre-monsoon in the country is quite high (7.8ºC) with a sharp jump from February to March (4.5ºC), whilst the maximum temperature peak in April (36.49ºC) indicates pre-monsoon instability. The 700hPa temperature shows a moderate correlation of 0.62 and 0.66 with lightning frequency and thunderstorm days, respectively. A strong SLP ridge from the northwest and 500hPa GpH ridge over northwest to south-eastern Bangladesh favors thunderstorm mediated severe pre-monsoon lightning. The low pressure trough over the Gangetic plains of India towards Bangladesh is a very unique characteristics for convective activities in May. The pre-monsoon lightning activity is also attributed by very strong temperature anomaly whilst the associated convective precipitation system is triggered by topographic forcing of the Shillong Plateau and Chittagong hill tracts. Southerly to south-westerly low level jet assist moisture transport from Bay of Bengal (BoB) in pre-monsoon. North to north-westerly subtropical jet stream provides conditions conducive to the development of pre-monsoon thunderstorms and resultant lightning activity. Moreover, CAPE all over the country in May destabilizes the country’s atmosphere with lots of thunderstorms. The precise information of pre-monsoon climatological anomaly can be beneficial for the management of direct-death related lightning disaster in Bangladesh.